The present invention relates to avionics systems and more specifically to instrument systems for measuring the thrust produced by aircraft engines.
It is important for the thrust developed by aircraft engines to be accurately and reliably measured in order to fix engine thrust ratings and assure airplane takeoff field length and climb out performance. Historically, gear driven turboprop powered aircraft have used torquemeters located on the turboshaft between the power producer and propeller to measure thrust. Shaft torque and RPM are then employed to determine the horsepower delivered to the propeller. For ungeared turboprop engines without a shaft drive and turbofan engines the pressure ratio across the core engine has been used to provide an indication of the power supplied by the system. In all such cases, windtunnel tests with scale models are commonly used to specify the conversion between shaft power and commanded thrust as delivered by the propellers or fan blades.
In operation these systems assume that uniform amounts of thrust are produced by the propeller system as determined by the operation of the power plant. No account is or can be made for variable losses due to deterioration of the propeller, gearbox or power turbine or for the full range of environmental conditions (e.g. icing) which may affect the propeller system. Therefore, the indicated thrust set in accordance with these systems may not accurately reflect the actual thrust produced.
It is, therefore, an object of the present invention to provide a system for accurately measuring the thrust produced by aircraft engines which rely on induced flow for their propulsive effect.
It is another object of the present invention to provide a thrust measuring system for turboprop engines which supplies measurements that directly reflect the actual thrust produced.
It is a further object of the present invention to provide a thrust measuring system for aircraft engines which is of comparatively simple design yet is accurate, reliable and effective under a full range of environmental conditions.